Fix flaky AsyncBatchWriteHandlerTest.correctlyLimitConcurrency

[scwhittle]

The test was expecting the future to be done but this is racy because though the handler has completed, the threads may not have finished and marked the future as completed.

Use the polling mechanism present in the test to verify the future is done instead.

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[gemini-code-assist]

Summary of Changes

Hello @scwhittle, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a known flakiness in a test case related to asynchronous batch write handling. The fix ensures the test reliably passes by introducing a polling mechanism for future completion, thereby eliminating race conditions that previously led to intermittent failures. This change improves the stability and trustworthiness of the test suite.

Highlights

• Flaky Test Fix: Addressed a flakiness issue in AsyncBatchWriteHandlerTest.correctlyLimitConcurrency which was caused by a race condition where the test asserted future completion too early, before background threads might have finished.
• Improved Assertion Logic: Replaced a direct assertThat(future).isDone() assertion with a polling mechanism using eventually(5, () -> assertThat(future).isDone()) to robustly verify future completion, accounting for asynchronous thread execution.
• Dependency Update: Added an import for java.util.concurrent.TimeUnit, likely to support the new polling mechanism or related timeout functionality.

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[github-actions]

Assigning reviewers:

R: @ahmedabu98 for label java.

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[Abacn]

Thanks!